The invention disclosed herein relates generally to cell search procedures for dual mode communication devices and, more particularly, to the detection of a radio access technology for a cell.
In order for a wireless communication device to connect with a communication network, the wireless communication device needs to find and acquire synchronization with a cell within the network, read system information from a broadcast channel in the cell, and perform a random access procedure to establish a connection with the cell. The first of these steps is commonly referred to as cell search. A cell search is typically performed on power-up when initially accessing the network. Additionally, mobile communication devices may perform a cell search after attaching to a network to identify candidate target cells for a hand over.
The details of a cell search will depend on the underlying radio access technology (RAT). In general, the cell search can be divided into three basic steps: (1) acquiring frequency and time synchronization; (2) acquiring frame timing of the cell, i.e., determining the start of the downlink frame; and (3) determining the identity of the cell. Typically, the base station transmits one or more synchronization signals. The mobile communication device scans a frequency band of interest and correlates the received signal with a primary synchronization signal. When a cell is detected, the mobile communication device performs time and frequency synchronization and determines the cell identity.
The problem of cell search becomes more complicated for dual mode or multi-mode communication devices that operate in frequency bands that deploy a mix of RATs. In such mixed environments, base stations may transmit signals of varying bandwidth in different frequency regions within the same frequency band. One example of such a mixed environment comprises a first group of base stations operating according to the Wideband Code Division Multiple Access (WCDMA) standard and a second group of base stations operating according to the Long-Term Evolution (LTE) standard. In order to perform a cell search on a candidate carrier frequency, the mobile communication device needs to know the correct RAT because different RATs have different cell search procedures.
A blind detection approach can be used to perform a cell search. With a blind detection approach, the mobile communication device scans a frequency band of interest and measures the received energy on a plurality of candidate frequencies. For each candidacy frequency, the mobile communication device successively attempts synchronization using different RATs until the synchronization is obtained. With the blind detection approach, the time needed to perform a cell search increases dramatically as the number of possible frequencies and RATs grows. Therefore, new techniques for identifying the RAT of a cell are needed to reduce the amount of time needed to perform cell search in heterogeneous networks employing a mix of RATs.